PMID: 44680Sep 29, 1979

A spin label study of horseradish peroxidase

Biochimica Et Biophysica Acta
G Rakhit, C F Chignell


The topography of the active sites of native horseradish peroxidase and manganic horseradish peroxidase has been studied with the aid of a spin-labeled analog of benzhydroxamic acid (N-(1-oxyl-2,2,5,5-tetramethylpyrroline-3-carboxy)-p-aminobenzhydroxamic acid). The optical spectra of complexes between the spin-labeled analog of benzhydroxamic acid and Fe3+ or Mn3+ horseradish peroxidase resembled the spectra of the corresponding enzyme complexes with benzhydroxamic acid. Electron spin resonance (ESR) measurement indicated that at pH 7 the nitroxide moiety of the spin-labeled analog of benzhydroxamic acid became strongly immobilized when this label bound to either ferric or manganic horseradish peroxidase. The titration of horseradish peroxidase with the spin-labeled analog of benzhydroxamic acid revealed a single binding site with association constant Ka approximately 4.7 . 10(5) M-1. Since the interaction of ligands (e.g. F-, CN-) and H2O2 with horseradish peroxidase was found to displace the spin label, it was concluded that the spin label did not indeed bind to the active site of horseradish peroxidase. At alkaline pH values, the high spin iron of native horseradish peroxidase is converted to the low spin form and the bindin...Continue Reading


Apr 15, 1987·Clinica Chimica Acta; International Journal of Clinical Chemistry·C HanquezN Cittanova
Apr 30, 1984·Biochemical and Biophysical Research Communications·G Rakhit, J P Hanig

Related Concepts

Hydrogen Peroxide
Cyclic N-Oxides
Complex (molecular entity)
Spin Labels
Free Radicals
Ligand Binding Domain
Compound A 12
N-(1-oxyl-2,2,5,5-tetramethylpyrroline-3-carboxy)-4-aminobenzhydroxamic acid

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